Over-the-wire rapid-exchange catheters are adaptable for various applications involving various body passageways or cavities, one of which is an intravascular procedure called percutaneous transluminal coronary angioplasty (PTCA) for dilatation of a coronary stenosis. During the performance of the PTCA procedure, it is often necessary to remove the operative catheter, whether diagnostic or therapeutic in nature, and replace it with another operative catheter.
In the performance of a typical PTCA procedure, a guiding catheter is percutaneously introduced into the cardiovascular system of the patient. This guiding catheter typically has a distal tip which is shaped to enhance its ability to be advanced to the vicinity of the selected treatment area. The guiding catheter can be twisted or rotated to orient the shaped distal tip to follow the vascular passageways as desired. The distal tip of the guiding catheter is advanced through the cardiovascular system to the aorta, near the ostium, or mouth, of the coronary artery to be inspected or treated. At this point, the shaped distal tip of the guiding catheter is oriented into the coronary ostium.
An operative catheter is then inserted into the guiding catheter and advanced to the treatment area. The guiding catheter will typically incorporate a releasable seal near its proximal end, to seal the guiding catheter around the operative catheter and prevent back leakage of contrast dye or other fluids. The seal is typically an O-ring which can have its internal opening tightened around the operative catheter. The tightness of the seal is selectively adjusted by the physician during the procedure as required to allow movement of the catheter or guidewire, and to maintain a fluid tight seal. The operative catheter can have various operative means on its distal end, for diagnostic or therapeutic purposes. Other procedures could utilize a laser source or an image guide, or other means as required, but in the case of the PTCA procedure, the operative means is an inflatable angioplasty balloon. In the typical over-the-wire procedure, the operative catheter has a guidewire running through an inner guidewire channel in the catheter body. This guidewire channel is usually separate from the operative or communicative channel which operates the operative means, such as by inflating the angioplasty balloon in the PTCA procedure.
The guidewire runs from the proximal end of the operative catheter, through the guidewire channel, and out the distal end of the catheter body. The distal tip of the guidewire is normally shaped to facilitate its advancement into the coronary artery to be treated. The distal tip of the guidewire is advanced out the distal end of the operative catheter, past the ostium of the coronary artery, along the selected coronary artery to the treatment point. The guidewire can be twisted or rotated as required to orient the shaped distal tip of the guidewire to facilitate passage through the artery. The operative catheter can be sequentially moved along with the guidewire, or the guidewire can be advanced alone, to be followed by the operative catheter. Many physicians prefer to sequentially advance the operative catheter to assist in guiding the guidewire tip. For example, when two or more curves in the vascular passageway are encountered, it is often helpful to advance the guidewire through the first curve and then bring the operative catheter over the guidewire into the first curve. Then, the guidewire is advanced through the second curve, assisted by the support of the operative catheter. This calls for smooth movement of the operative catheter and guidewire, without interference from any unnecessary drag from the releasable seal, to allow the physician to feel the progress of the guidewire and catheter.
Eventually, in the PTCA procedure, the distal tip of the guidewire is advanced through the stenosis in the coronary artery. The operative dilatation catheter is then advanced over the guidewire until the balloon on the distal end of the operative catheter is positioned across the stenosis. The balloon is then inflated to dilate the stenosed area of the artery, deflated, and withdrawn to allow the resumption of blood flow. It is often necessary to withdraw the operative catheter and replace it with a second operative catheter to perform a different procedure, or to more effectively perform the procedure at hand. An example of the need for such an exchange can be to replace the balloon with a balloon of a different size.
Catheters have been devised which will allow the removal of the first operative catheter while holding the guidewire in place, followed by the insertion of a second operative catheter over the original guidewire. During this procedure, called a rapid exchange, it is still necessary to feel the advance of the operative catheter through the vascular passageways. It is also necessary to hold the guidewire in place, to avoid the time and risk involved in inserting a second guidewire, and to prevent the guidewire from partially withdrawing with the catheter. Most rapid exchange catheters have simply used a guidewire channel located near the distal end of the catheter body, through which the guidewire is threaded. From this distal guidewire channel, the guidewire typically simply passes alongside the catheter body to the proximal end of the catheter. This allows the physician to hold the guidewire in place while withdrawing the operative catheter until the distal guidewire channel has exited the guiding catheter. The physician can then grasp the guidewire distally from the distal end of the operative catheter and fully withdraw the operative catheter over the proximal end of the guidewire. The proximal end of the guidewire is then inserted through the distal guidewire channel on the replacement operative catheter, and the catheter is inserted to the treatment area over the guidewire.
The principal problem with such rapid exchange catheters is that the guidewire passes alongside the catheter body over most of its length. This means that the releasable seal in the guiding catheter must seal against the guidewire by pressing the guidewire against the outer surface of the operative catheter. This can require a tighter pressure by the sealing O-ring than would be required if the O-ring were in full contact with the outer wall of the catheter around its circumference. This creates a significant drag on the guidewire, which interferes with the physician's tactile feedback during initial insertion of the guidewire from the coronary ostium to the stenosis, and it can even increase the drag on the operative catheter during insertion over the guidewire. Both of these conditions are undesirable, especially at this particular juncture in the PTCA procedure, when the physician particularly needs the maximum possible tactile feedback.
In addition, it is difficult to coordinate the advancement of the catheter and separate guidewire through the guiding catheter. Finally, when the releasable seal is tightened against the catheter and guidewire, such as during dye injection, the guidewire exits the guiding catheter at an extreme angle relative to the operative catheter, which feels awkward to the physician.
Therefore, it is an object of the present invention to provide an over-the-wire rapid-exchange catheter which will allow the physician increased tactile feedback during advancement of the guidewire from the distal mouth of the guiding catheter through the stenosis and during advancement of the operative catheter over the guidewire. It is a further object of the present invention to provide an over-the-wire rapid-exchange catheter in which the guidewire does not contact the releasable seal in the guiding catheter, during advancement of the guidewire distal tip out of the distal end of the guiding catheter, and which presents a smooth sealing surface to the releasable seal.